Relative Charge, Mass & Atomic Numbers
Chemistry: Cambridge International GCSE Supplement, topic 2.2.2
Atomic Structure: Relative Charge, Mass & Atomic Numbers
Atoms have protons, neutrons, and tiny electrons. Proton number defines the element. Mass number is protons + neutrons. Relative charge and mass describe particles in the atom.
Particles in an atom
- Atoms contain protons, neutrons, and electrons.
- Protons have a relative charge of +1.
- Neutrons have no charge, so their relative charge is 0.
- Electrons have a relative charge of -1.
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Relative mass of particles
- Protons have a relative mass of 1.
- Neutrons have a relative mass of 1, similar to protons.
- Electrons have a much smaller relative mass, about 1/1836.
- Atoms are mostly mass in their nucleus, where protons and neutrons exist.
Proton number (Atomic number)
- The proton number is the number of protons in an atom's nucleus.
- Proton number defines the element (e.g., carbon always has 6 protons).
- Proton number is also called atomic number.
Mass number (Nucleon number)
- The mass number is the total protons and neutrons in the nucleus.
- Mass number = number of protons + number of neutrons.
- This number tells the mass of the nucleus but ignores electrons.
- Example: Carbon-12 has 6 protons and 6 neutrons, so mass number = 12.
Summary of atomic numbers and mass
- Atomic number = number of protons, identifies the element.
- Mass number = protons + neutrons, which shows the atom's mass.
- Relative charge and mass help describe particles in the atom.
Test yourself on Relative Charge, Mass & Atomic Numbers
Which subatomic particles have a relative mass of 1?